17β-Hydroxysteroid dehydrogenase
class of enzymes
17β-Hydroxysteroid dehydrogenases (17β-HSD, HSD17B) (EC 1.1.1.51), also 17-ketosteroid reductases (17-KSR), are a group of alcohol oxidoreductases which catalyze the reduction of 17-ketosteroids and the dehydrogenation of 17β-hydroxysteroids in steroidogenesis and steroid metabolism. This includes interconversion of DHEA and androstenediol, androstenedione and testosterone, and estrone and estradiol.
The major reactions catalyzed by 17β-HSD (such as the conversion of androstenedione to testosterone) are hydrogenation (reduction) reactions, rather than dehydrogenation (oxidation) reactions.
Reactions
17β-HSDs catalyze the following redox reactions of sex steroids:
20α-Hydroxyprogesterone ↔ Progesterone
DHEATooltip Dehydroepiandrosterone ↔ Androstenediol
Androstenedione ↔ Testosterone
Dihydrotestosterone ↔ 5α-Androstanedione / 3α-Androstanediol / 3β-Androstanediol
Estrone ↔ Estradiol
16α-Hydroxyestrone ↔ Estriol
Activity distribution
Genes
Genes coding for 17β-HSD include:
HSD17B1: Referred to as "estrogenic". Major subtype for activation of estrogens from weaker forms (estrone to estradiol and 16α-hydroxyestrone to estriol). Catalyzes the final step in the biosynthesis of estrogens. Highly selective for estrogens; 100-fold higher affinity for estranes over androstanes. However, also catalyzes the conversion of DHEA into androstenediol. Recently, has been found to inactivate DHT into 3α- and 3β-androstanediol. Expressed primarily in the ovaries and placenta but also at lower levels in the breast epithelium.
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